Screen-analysis based device security

ABSTRACT

Systems and methods are provided for a content-based security for computing devices. An example method includes identifying content rendered by a mobile application, the content being rendered during a session, generating feature vectors from the content and determining that the feature vectors do not match a classification model. The method also includes providing, in response to the determination that the feature vectors do not match the classification model, a challenge configured to authenticate a user of the mobile device. Another example method includes determining a computing device is located at a trusted location, capturing information from a session, the information coming from content rendered by a mobile application during the session, generating feature vectors for the session, and repeating this until a training criteria is met. The method also includes training a classification model using the feature vectors and authenticating a user of the device using the trained classification model.

BACKGROUND

The use of mobile devices, such as smart phones, wearable devices,tablets, laptops, etc., has been increasing. These mobile devices canstore information that a user considers personal or private. A mobiledevice that falls into the wrong hands can result in a bad actor havingaccess to that information. While security measures, such as biometricsand passwords, are available to protect access to mobile devices suchmeasures can be seen as cumbersome to users who use a mobile devicefrequently throughout the day, and may be disabled.

SUMMARY

Implementations learn the behavior and preferences of the deviceowner(s) and use these signals to detect outlier activity. In otherwords, the mobile device can use a classification model (e.g. a machinelearning algorithm) to detect actions that are not typical for theowner. Initially, the mobile device trains the model by extractingfeatures from content displayed on the screen during sessions that occurin a trusted environment. The trusted environment may exist when thedevice is located at a safe location, such as the user's home orworkplace, or after the user enters a password or series of passwords. Asession can be one screen or a series of screens rendered by use of themobile device. Thus, a session captures content rendered by mobileapplications used by the user on the device. After an initial trainingof the classification model, the device may use the model to analyzecurrent sessions, e.g., current activity. This is an inference stage.Further training may occur when the device is in a safe or trustedenvironment, but after the initial training the device is capable ofentering the inference stage. During the inference stage when contentfor a session fails to meet a confidence level the device may issue achallenge. In other words, during use of the device, the classificationmodel may determine that the current activity (or a series ofactivities) represents outlier activity. The challenge may be designedto authenticate the user. The challenge can be passcode-based or can bebased on past authenticated sessions of the owner. For example achallenge may ask which person the owner talked to at a particular timeor may ask the owner to complete information obscured in a screenrecently viewed, e.g., during a session that was consistent with themodel. If the challenge is met, i.e., if the user answers correctly, thedevice may update the classification model with the content from thechallenged session. For example, the features generated from thechallenged session may be used as positive examples to further train theclassifier. If the challenge is not met, the device may enter a lockmode.

In one general aspect, a mobile device includes at least one processorand memory storing instructions that, when executed by the at least oneprocessor, cause the mobile device to perform operations. The operationsinclude identifying content rendered by a mobile application, thecontent being rendered during a session, generating feature vectors fromthe content and determining that the feature vectors do not match aclassification model. The operations also include providing, in responseto the determination that the feature vectors do not match theclassification model, a challenge configured to authenticate a user ofthe mobile device.

In another general aspect, a method may comprise determining that amobile device is located at a trusted location, capturing informationfrom a session, the information coming from content rendered by a mobileapplication running on the mobile device during the session, andgenerating feature vectors for the session. The method also includesrepeating the capturing and determining until a training criteria is metand authenticating a user of the mobile device using the trainedclassification model.

In other general aspects, a mobile device comprises at least oneprocessor and memory storing instructions that, when executed by the atleast one processor, cause the mobile device to perform operations. Theoperations may include identifying content rendered by a mobileapplication, the content being rendered during a session, and generatingfeature vectors from the content. The operations may also includeapplying a classification model to the feature vectors, determiningwhether the feature vectors match a first user profile based onapplication of the classification model, the first user profilediffering from a second user profile, the mobile device being currentlyassociated with the second user profile, and initiating a profile switchresponsive to determining that the feature vectors match the first userprofile.

In one general aspect, a computer program product embodied on acomputer-readable storage device includes instructions that, whenexecuted by at least one processor formed in a substrate, cause acomputing device to perform any of the disclosed methods, operations, orprocesses. Another general aspect includes a system and/or a method fortraining a classification model using features generated from contentrendered by applications as the user uses the computing device and usingthe classification model to pass a challenge when atypical usage isrecognized, substantially as shown in and/or described in connectionwith at least one of the figures, and as set forth more completely inthe claims.

One or more of the implementations of the subject matter describedherein can be implemented so as to realize one or more of the followingadvantages. As one example, the device can be protected from continuedaccess by anyone but the owner even if the owner did not set up apassword or even if the password has been compromised. As anotherexample, the protection is unobtrusive. This means that the protectionoccurs mostly in the background, without user direction, and createsminimal overhead on the user. As another example, implementationsprovide an unobtrusive way to switch user profiles on a device shared bymultiple users. The content-based security system is based on contentpresentation on the screen and therefore does not rely on theapplication rendering the content to provide any of the functionalitydescribed herein. In other words, the system functions for allapplications and thus all activity performed on the mobile device.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features will beapparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example system in accordancewith the disclosed subject matter.

FIG. 2 is a block diagram illustrating another example system inaccordance with the disclosed subject matter.

FIG. 3 illustrates a flow diagram of an example process for usingscreen-analysis to enhance device security, in accordance with disclosedimplementations.

FIG. 4 is an example display of a mobile computing device with alow-level content-based challenge.

FIG. 5 is an example display of a mobile computing device with ahigh-level content-based challenge.

FIG. 6 illustrates a flow diagram of an example process for training aprofile classification model, in accordance with disclosedimplementations.

FIG. 7 illustrates a flow diagram of an example process for usingscreen-analysis to enhance device security in a multi-user environment,in accordance with disclosed implementations.

FIG. 8 shows an example of a computer device that can be used toimplement the described techniques.

FIG. 9 shows an example of a distributed computer device that can beused to implement the described techniques.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of a content-based security system inaccordance with an example implementation. The system 100 may be used todetect unusual or outlier activities performed on a mobile device andprovide a challenge after detecting such activity. The outlier activitymay be determined based on a classification model trained using contentrendered while the device is used in a trusted environment. Thechallenge may also be based on content rendered for display on themobile device. The content-based security system may create minimaloverhead for the user, as it runs in the background and can providesecurity for a mobile device with or without use of a password. Thesystem 100 in FIG. 1 can by a client-server system, with some dataprocessing or data storage occurring at a server 170. However, otherconfigurations and applications may be used. For example, the dataprocessing and data storage can occur exclusively on the mobile device110. In some implementations, a user of the mobile device 110 mayindicate that portions of the processing be performed at the server 170.Thus, implementations are not limited to the exact configurationsillustrated.

The mobile content-based security system 100 may include a mobile device110. Mobile device 110 may be any mobile personal computing device, suchas a smartphone or other handheld computing device, a tablet, a wearablecomputing device, etc., that operates in a closed mobile environmentrather than a conventional open web-based environment. Mobile device 110may also be other types of electronic computing devices, such as alaptop or net-based computer. Mobile device 110 may be an example ofcomputer device 800, as depicted in FIG. 8 . Mobile device 110 may be amobile computing device used by a single user, or can be a mobile deviceshared by multiple users.

Mobile device 110 may include one or more processors formed in asubstrate configured to execute one or more machine executableinstructions or pieces of software, firmware, or a combination thereof.The processors can be semiconductor-based—that is, the processors caninclude semiconductor material that can perform digital logic. Themobile device 110 may thus include one or more computer memoriesconfigured to store one or more pieces of data, either temporarily,permanently, semi-permanently, or a combination thereof. The mobiledevice 110 may thus include applications 120, which represent machineexecutable instructions in the form of software, firmware, or acombination thereof. The components identified in the applications 120may be part of the operating system or may be applications developed torun using the operating system. In some implementations, applications120 may be mobile applications. Conventionally, mobile applicationsoperate in a closed environment, meaning that the user employs separateapplications to perform activities conventionally performed in aweb-based browser environment. For example, rather than going tobookit.com to book a hotel, a user of the mobile device 110 can use amobile application in applications 120 provided by bookit.com.Applications 120 may also include web applications, which may mirror themobile application, e.g., providing the same or similar content as themobile application. In some implementations, the applications 120 mayinclude functions performed by an operating system of the mobile device110.

The applications 120 may include a screen capture engine 126, a screenanalysis engine 122, and a screen-based security engine 124. In someimplementations, one or more of these applications can be provided bythe operating system of the mobile device 110. In some implementations,one or more of these applications can be downloaded and installed by theuser.

The screen capture engine 126 can include various functionalities. Insome implementations, the screen capture engine 126 may be configured toget textual information represented on the screen from an applicationprogram interface (API). In some implementations, the screen captureengine 126 may be built into the operating system, which can determinethe content of text fields displayed on the current screen. The textualinformation may be considered screen captured content, and each call tothe API or each time the content of text fields is determined may beconsidered a screen capture. In some implementations, the screen captureengine 126 may be configured to capture the screen by copying or readingthe contents of the device's frame buffer. Thus, the captured screen maybe an image and may be referred to as a captured image. The screencapture engine 126 may capture the screen at intervals. The interval canbe small, for example every half second or every second. In someimplementations, the screen capture engine 126 may be configured tocapture the screen every time a touch event occurs (e.g., every time theuser touches the screen to scroll, zoom, click a link etc.), in responseto an explicit user request or command, or when the device transitionsfrom one mobile application to another mobile application. In someimplementations, the screen capture engine 126 may increase the intervalat which a screen capture occurs when the screen does not change. Inother words, when the screen is static, the screen capture engine 126may capture images less often. The screen capture engine 126 may providethe captured content or screen images and metadata to a recognitionengine, which may be part of the screen capture engine 126 and locatedon the mobile device 110 or a server, such as server 170. If a screencapture image is provided to the recognition engine, the recognitionengine may identify words, entities, logos, etc. in the content of thescreen capture image. Thus, the recognition engine may generaterecognized content, which can be from words as well as images. Themetadata may include the timestamp, the mobile device type, a mobiledevice identifier, the mobile application running when the content wascaptured, e.g., the application that rendered the content displayed onthe screen, etc. In some implementations, the metadata may also includewhich applications are active, the location of the device, ambientlight, motion of the device, etc. The system may use this additionaldevice information to assist in content analysis (e.g., entitydisambiguation), feature generation (e.g., deciding what content is mostrelevant), etc. The recognition engine may thus be configured to performvarious types of recognition, such as character recognition, imagerecognition, logo recognition, etc., using conventional or laterdeveloped techniques.

The mobile device 110 may also include a screen analysis engine 122. Thescreen analysis engine 122 may be configured to determine a session andgenerate features based on the content identified in the session. Asession is one or more screen capture content events. In other words, asession can be the captured content from one screen capture image or aseries of related screen capture images (e.g., images captured during aspecified window of time, images captured during performance of anaction, images captured while a particular user interface element isused, images captured during usage of a particular application, imagescaptured during a particular task, etc.). Likewise, a session can alsobe content from one API call or a series of API calls, etc. The screenanalysis engine 122 may generate feature vectors for a session. Featuresinclude data items identified by the screen capture engine 126 in thecaptured content included the session and the metadata for the capturedcontent. For example, features can include entities, words, or images,pixels, or image features identified in the content, the applicationthat rendered the content, the date/time, whether the device was moving(e.g., in a car), etc. The information about one feature may be combinedin a feature vector and many feature vectors may be concatenated into anaggregate feature vector a session. The screen analysis engine 122 mayprovide the aggregate feature vector, or in other words the variousindividual feature vectors, to a classification model, either fortraining purposes or for analysis.

A classification model, such as prediction classifier 134, is any typeof machine-learning classifier, such as a long short-term memory (LSTM)neural network, feed-forward neural network, a support vector machine(SVM) classifier, etc., that is either a binary classifier (for a devicewith one user) or a multi-class classifier (for a device with multipleusers). The classification model has two modes, a training mode and aninference mode. In the training mode the screen analysis engine 122 usesfeature vectors generated from captured content, (e.g., contentdisplayed on the mobile device) as positive training examples for theclassification model. When enough training data has been collected, thescreen analysis engine 122 may obtain generic negative examples or mayintelligently permute the positive examples to generate negativeexamples. For example, the screen analysis engine 122 may replace someof the words/entities in captured content with similar words/entities.As one example, a place or person may be replaced with another place orperson. When the model is a multi-class classifier the system may usepositive examples for one user as the negative examples for anotheruser. In some implementations, the screen may train the model withoutnegative examples. The screen analysis engine 122 may then train theclassification model using the positive and negative examples (wherenegative examples are used). Training the classification model createsthe prediction classifier 134, which may then be used in an inferencemode. The screen analysis engine 122 may continue training of theclassification model, for example with additional positive examples, torefine the model.

In some implementations, the system may train multiple classificationmodels. For example, one model may be used for content rendered by aparticular application or a particular application category. Forinstance, one model may be used for games and another model may be usedfor news applications. Thus, the prediction classifier 134 may representmore than one trained classifier.

In some implementations, the screen capture engine 126 can include anindexing engine configured to index the captured content. The index mayalso associate a screen capture image with the text, entities, images,logos, etc. identified in the image. Thus, for example, the indexingengine may generate index entries (e.g., stored in screen capture index146) for a captured image and captured content. In some implementationsthe indexing engine may be on a server, such as server 170, and thescreen capture engine 126 may provide the captured image and capturedcontent to the server. The index may be an inverted index, where a keyvalue (e.g., word, phrase, entity, image, logo, etc.) is associated witha list of images (e.g., copies of the captured screen images) thatinclude the key value. The index may include metadata (e.g., where onthe captured image the key value occurs, a rank for the key value forthe image, etc.) associated with each captured image in the list. Insome implementations, the index may also include a list of capturedimages indexed by a timestamp. The indexing engine may store the indexin memory, for example in screen capture index 146. Of course, in someimplementations the system may store the index in a user account on aserver in addition to or instead of on the mobile device 110. The userof the mobile device 110 may control when the screen capture engine 126is active. For example, the user may specify that the screen captureengine 126 is active only when other specified mobile applications 120are running (e.g., only when in a social media mobile application). Theuser may also manually turn the screen capture engine 126 on and off,for example via a settings application. In some implementations, theuser may invoke the screen capture engine 126 with a gesture or action.Disabling the screen capture engine 126 may also disable thescreen-based security measures described herein.

The applications 120 may also include screen-based security engine 124.The screen-based security engine 124. The screen-based security engine124 may use the prediction classifier 134 in an inference mode toprovide unobtrusive security for the mobile device 110. The screen-basedsecurity engine 124 may receive session-based features from the screenanalysis engine 122 and the screen capture engine 126 and run thefeatures against the prediction classifier 134. If the predictionclassifier 134 indicates the features are outliers (e.g., do not fitinto the model with a sufficient confidence level), the screen-basedsecurity engine 124 may offer a challenge to the user. The challenge canbe password-based (e.g., requesting the user enter a password) orcontent-based (e.g., based on information found in the screen captureindex 146 or the session features 132).

A content-based challenge is useful as it can be used to identify a badactor who has hacked or stolen the user's password. The information inthe session features 132 include features extracted from contentgenerated at a trusted location and/or content generated for a pastsession that did not fall outside the confidence level for theprediction classifier 134. In other words, the information in thesession features 132 represents information from a verified session,e.g., matching a trusted location or matching the classification model,and are typical for the user of the mobile device 110, not outlieractivity. The screen capture index 146 may include a copy of apreviously captured screen and key items, such as words, entities, orpictures, identified in captured content.

The screen-based security engine 124 may use information from thesession information feature 132 and/or the screen capture index 146 togenerate a content-based challenge. For example, the screen-basedsecurity engine 124 can present a previously captured screen (e.g., fromscreen capture index 146) with one or more key items obscured andrequest that the user provide the obscured information. As anotherexample, the screen-based security engine 124 may extract high levelinformation from the session features 132 or the screen capture index146. For example, the screen-based security engine 124 may ask whichperson a user talked to or texted last night, which entity the usersearched for two days ago, what restaurant the user frequents mostoften, what application the user typically uses for a task (e.g., forreading email or booking a restaurant), etc. The content-basedchallenges provide additional layers of security that protect a devicewithout a password or a device where the password has been stolen orhacked.

The mobile device 110 may include data stores 130, which are stored inthe memory of the mobile device 110 and used by the applications 120. Insome implementations, the data stores 130 may include a screen captureindex 146 which includes items identified in the screen capture images,and a data graph 144. The data graph 144 may be a graph-based data storethat stores data and rules that describe knowledge about the data in aform that provides for deductive reasoning. For example, in a knowledgebase, information may be stored about entities in the form ofrelationships to other entities. An entity may be may be a person,place, item, idea, topic, word, phrase, abstract concept, concreteelement, other suitable thing, or any combination of these. Entities maybe related to each other by labeled edges that represent relationships.The labeled edges may be directed or undirected. For example, the entityrepresenting the National Football League may be related to a Jaguarentity by a “has team” relationship. The data graph 144 may be a subsetof entities and relationships in a larger knowledge base located atserver 170, especially if the large knowledge base includes millions ofentities and billions of relationships. For example, the entities andrelationships in the data graph 144 may represent the most popularentities and relationships from a knowledge base, or may be selectedbased on user preferences. For example, if the user has a profile,entities and relationships may be selected for inclusion in data graph144 based on the profile or based on the types of entities frequentlyidentified in the content of the screen capture images. In someimplementations the data graph 144 may include entities frequentlyrecognized in the content of screen capture images. Such entities may beconsidered personal entities, i.e., entities the user interacts withfrequently but are not well known to the public at large. Thus, datagraph 144 may include entities not necessarily found in a large publicknowledge base. Such personal entities may include people as well asphone numbers, addresses, cities, etc. the user interacts with often.

The data stores 130 may also include session features 132. The sessionfeatures 132 may represent positive examples, e.g., features identifiedfrom content generated in a trusted environment. A trusted environmentmay be a location identified as trusted by the user of the mobile device110, or an environment that exists after the user has entered apassword, or a combination of these. The session features 132 may beused to train the prediction classifier 134 and/or to provideinformation used in a challenge. The session features 132 may alsoinclude features generated during a session that the classificationmodel determined to be consistent with the activities of the user. Insome implementations, the system may have a higher threshold for storingthese features than the threshold used to determine whether a session isconsistent with the profile. In other words, to be included in sessionfeatures 132, the confidence level must be higher than for the featuresto be considered typical for the user.

The data stores 130 may also include profile data 142. The profile data142 may include information about a user of the mobile device. Forexample, profile data 142 may include locations considered trusted(e.g., the user's work or home), password data, preferences, and otherdata typical for a user account or profile. In some implementations, thescreen capture index 146, the data graph 144, and the profile data 142may also reside on server 170, e.g., in an account associated with theuser of the mobile device 110. In some implementations, the screencapture index 146, data graph 144, and profile data 142 may be copies ofor subsets of data stored on the server 170 or in another locationspecified by the user. The data stores 130 may be stored on anynon-transitory memory.

In a mobile device 110 that has several users, such as a shared familytablet or laptop, each user may have a respective data store 130. Inother words, each user may have an individual copy of the screen captureindex 146, the profile data 142, and the session features 132. In suchan implementation, the prediction classifier 134 may be a multi-classclassifier, able to analyze captured content for a current session andclassify the content as fitting one of two or more profiles, or asfitting none of the profiles (e.g., outlier activity). In such animplementation, each user may initiate a training session for theprediction classifier 134 via the screen analysis engine 122.

The mobile content-based security system 100 may include a server 170,which may be a computing device or devices that take the form of anumber of different devices, for example a standard server, a group ofsuch servers, or a rack server system. For example, server 170 may beimplemented in a distributed manner across multiple computing devices.In addition, server 170 may be implemented in a personal computer, forexample a laptop computer. The server 170 may be an example of computerdevice 800, as depicted in FIG. 8 , or computer device 900, as depictedin FIG. 9 . Server 170 may include one or more processors formed in asubstrate configured to execute one or more machine executableinstructions or pieces of software, firmware, or a combination thereof.The processors can be semiconductor-based—that is, the processors caninclude semiconductor material that can perform digital logic.

The server 170 can also include one or more computer memories. Thememories, for example, a main memory, may be configured to store one ormore pieces of data, either temporarily, permanently, semi-permanently,or a combination thereof. The memories may include any type of storagedevice that stores information in a format that can be read and/orexecuted by the one or more processors. The memories may includevolatile memory, non-volatile memory, or a combination thereof, andstore modules or engines that, when executed by the one or moreprocessors, perform certain operations. In some implementations, themodules may be stored in an external storage device and loaded into thememory of server 170. In some implementations, server 170 may storebackup copies of one or more of the information files in data store 130,may provide source data for one or more of the information files in datastore 130, and/or may perform one or more of the functions of the screencontent engine.

FIG. 2 is a block diagram illustrating an example system in accordancewith the disclosed subject matter. FIG. 2 illustrates an implementationof system 100 with one or more of the functions of the screen contentengine 250 occurring at the server 170. For example, the screen contentengine 250 may receive a screen capture image from the screen captureengine 126 on mobile device 110 and may perform the recognition toidentify key items in the image and may index the image with the keyitems. In some implementations, the screen content engine 250 maygenerate feature vectors for the image or a series of images. In otherwords, the screen content engine 250 may generate feature vectors for asession, as described above.

The server 170 may store knowledge base 210. The knowledge base 210 maybe a large graph-based data store that stores data and rules thatdescribe knowledge about the data in a form that provides for deductivereasoning. A knowledge base with a large number of entities and even alimited number of relationships may have billions of connections. Insome implementations, knowledge base 210 may be stored in an externalstorage device accessible from server 170 and/or mobile device 110. Insome implementations, the knowledge base 210 may be distributed acrossmultiple storage devices and/or multiple computing devices, for examplemultiple servers. The entities and relationships in the knowledge base210 may be searchable, e.g., via an index. For example, the index mayinclude text by which an entity has been referred to. Thus, reference tothe knowledge base 210 may be understood to include an index thatfacilitates finding an entity using a text equivalent.

The screen content engine 250 may include components that analyze thescreen content in a screen capture image and to identify key items, suchas words, entities, logos, etc., in the screen content. Identifiedentities may be entities that are in the knowledge base 210.Accordingly, the screen content engine 250 can be configured to performvarious types of recognition, such as character recognition, imagerecognition, logo recognition, etc., using conventional or laterdeveloped techniques. The screen content engine 250 may match the itemsidentified (e.g., text, images, logos) to entities in the knowledge base210. In some implementations, the screen content engine 250 may indexthe key items, as discussed above, storing the inverted index in screencapture index 215. The screen capture index 215 is associated with auser of the mobile device 110. In some implementations, the screencontent engine 250 may also generate session features 225, similar tosession features 132 of FIG. 1 . In some implementations, the sessionfeatures 225 may be transmitted to the server 170 from the mobile device110. In other words, the screen analysis engine 122 may generate thefeatures and may transmit the features to the server 170, where they arestored as positive examples for the user. In some implementations, thescreen content engine 250 may determine when a sufficient quantity ofpositive examples exists for training the model. In someimplementations, the screen content engine 250 may reserve a quantity ofpositive examples and evaluate the model against the examples. In suchimplementations, the screen content engine 250 may determine when themodel has a sufficient classification error (e.g., 95% accuracy or 99%accuracy, etc.) In some implementations, the server 170 may store a userprofile 220. The user profile may include information similar to profiledata 142.

Returning to FIG. 1 , the mobile device 110 may be in communication withthe server 170 and with other mobile devices over network 160. Network160 may be for example, the Internet, or the network 160 can be a wiredor wireless local area network (LAN), wide area network (WAN), etc.,implemented using, for example, gateway devices, bridges, switches,and/or so forth. Network 160 may also represent a cellularcommunications network. Via the network 160 the server 170 maycommunicate with and transmit data to/from mobile device 110 and mobiledevice 110 may communicate with other mobile devices (not shown).

The mobile content-based security system 100 represents one exampleconfiguration and implementations may incorporate other configurations.For example, some implementations may combine one or more of thecomponents of the screen capture engine 126, the screen analysis engine122, or the screen-based security engine 124 into a single module orengine. Similarly, some implementations may combine one or more of thescreen capture engine 126, the screen analysis engine 122, and thescreen-based security engine 124 into a single module or application.Furthermore, one or more of the components of the screen capture engine126, the screen analysis engine 122, or the screen-based security engine124 may be performed at the server 170. As another example one or moreof the data stores, such as the screen capture index 146, the data graph144, the profile data 142, and the session features 132, or theprediction classifier 134 may be combined into a single data store ormay distributed across multiple computing devices, or may be stored atthe server 170 or another location specified by the user.

To the extent that the mobile content-based security system 100 collectsand stores user-specific data or may make use of personal information,the users may be provided with an opportunity to control whetherprograms or features collect the user information (e.g., informationabout a user's social network, social actions or activities, a user'spreferences, or a user's current location), or to control whether and/orhow to store screen capture images and content. For example, the systemmay refrain from capturing content for certain applications, such asbanking applications, health applications, or other similar applicationsor where capturing such content violates terms of service. In addition,the user may be provided with the opportunity to disable capturingscreen content for specific applications or categories of applications.In addition, certain data may be treated in one or more ways before itis stored or used, so that personally identifiable information isremoved. For example, a user's identity may be treated so that nopersonally identifiable information can be determined for the user, or auser's geographic location may be generalized where location informationis obtained (such as to a city, ZIP code, or state level), so that aparticular location of a user cannot be determined. Thus, the user mayhave control over how information is collected about the user and usedby a mobile content-based security system.

FIG. 3 illustrates a flow diagram of an example process for usingscreen-analysis to enhance device security, in accordance with disclosedimplementations Process 300 may be performed by a mobile content-basedsecurity system, such as system 100 of FIG. 1 or FIG. 2 . Process 300may be used to provide unobtrusive security or backup security in amobile environment, ensuring that a bad actor cannot continue to accessthe mobile device. Process 300 may begin by training a predictionclassifier with session information captured on a mobile device (305).This is a training mode for the device and may take place when thedevice is in a trusted environment, as explained in more detail withregard to FIG. 4 .

Once the classification model is trained, the system may enter aninference mode using the classification model. The inference mode mayrun until the user provides instructions to quit the inference mode oruntil the device enters a locked mode. Thus, the inference mode mayprotect a device even when the device is not locked with a password,i.e., a password is not needed to activate the device from a sleep orinactive mode. Even when the device is protected with a password, theinference mode protects the content of the device if the password iscompromised or stolen.

In the inference mode, the system may classify a current session usingthe classification model (310). The session can be one screen or aseries of related screens. Thus, the session represents content renderedby a mobile application and displayed on the mobile device. To classifythe current session, the system may perform recognition on the capturedscreen image(s) that make up the session to identify content (e.g., keyitems) displayed in the screen capture image(s). The system may alsorecognize entities in the captured content, whether text-based orrecognized from the image. The system may generate feature vectors fromthe captured content and provide the feature vectors, e.g., in the formof an aggregated feature vector, to the classification model. Theclassification model may determine how well the features fit the trainedmodel (315). In other words, the classification model takes the featurevectors and determines a confidence score that reflects how well thefeatures fit within the model. The system may determine whether thesession has low confidence based on the current session alone, or basedon a mean of confidence scores for sessions occurring over a window oftime. If the confidence score or the mean confidence score meets orexceeds a threshold (315, No), the features are consistent with themodel and the system may continue classifying sessions (310). If theconfidence score for the current session or the mean confidence scoreover a window of current sessions fails to meet the threshold (315,Yes), the system may determine that the activity is an outlier and mayrepresent the activity of an unauthorized user.

Accordingly, the system may present a challenge to the user (320). Insome implementations, the challenge may be to enter a pre-set password.In other implementations, the challenge may be based on captured contentassociated with a previous session that did meet the confidencethreshold (320). In some implementations, the challenge may include acombination of the password and challenge questions based on capturedcontent associated with previous sessions. The previous session shouldbe a session that occurred a few hours before the current session, butpreferably no earlier than a couple of days prior to the currentsession. This ensures that the legitimate user can remember whatoccurred in the previous session but that the session did not occurrecent enough for an unauthorized user to view it.

The challenge can be one question or a series of questions. In otherwords, to avoid a lucky guess, the system may present a series ofquestions as the challenge and require the user to answer at least amajority (e.g., 2 of 3) right to meet the challenge. The challengequestions may be formed from content associated with the previoussession. In some implementations, the series of questions can be acombination of a password-based challenge and one or morecaptured-content based challenges.

FIG. 4 is an example display 400 of a mobile computing device with alow-level content-based challenge. The display 400 is an example of achallenge based on a previously viewed screen capture image. Thepreviously viewed screen may be stored, for example, as part of an indexof captured screens, for example screen capture index 146 of FIG. 1 orscreen capture index 215 of FIG. 2 , or as part of session information,such as session features 132 of FIG. 1 or session features 225 of FIG. 2. The previously viewed screen image may have been captured during asession or a window of sessions that was consistent with theclassification model and/or that occurred in a trusted environment. Insome implementations, the previously viewed screen may have a timestampthat is at least a minimum number of hours in the past. The minimum islong enough to ensure that the image is from a previous period of use ofthe device. A period of use may be defined, for example, as the periodbetween the device entering an inactive state. The device enters aninactive state when a user fails to interact with the device within apredefined time period. Conventionally, the user must tap or swipe thetouch-screen to reactivate the device.

To generate the challenge, the system may obscure portions 405 of thepreviously viewed screen image. For example, the words under portions405 a and 405 b are obscured. A portion 405 may be selected as being ahighly topical entity appearing in the previously viewed screen captureimage. The system can determine highly topical entities usingconventional entity detection and language analysis techniques. Thesystem may provide an instruction window 410 that informs the user howto meet the challenge. For example, the instruction window 410 mayrequest that the user provide the text corresponding to the obscuredportions. In the example of display 400, the system provides a text boxfor the user to provide text corresponding to portions 405 a and 405 b.However, the system may also offer a multiple choice question thatallows the user to select one of the offered choices. In addition, theobscured portion need not be text. The system can select an image toobscure and offer multiple images for the user to select. When the userhas provided a response for each obscured portion 405, the user mayselect or activate a control provided, for example in the instructionwindow 410, to submit the response to the challenge.

FIG. 5 is an example display of a mobile computing device with ahigh-level content-based challenge. The display 500 is an example of achallenge based on previous activity, not necessarily a singlepreviously viewed screen capture image. For a high-level content-basedchallenge, the system may access information from a previous sessionthat was consistent with the classification model and/or that occurredin a trusted environment. The information may be obtained, for example,from session features extracted during the previous session. Like thelow-level content-based challenge, the session may be associated with atime stamp that is at least a minimum number of hours in the past. Thehigh-level content-based challenge may thus be based on past analysis ofscreen capture images. The system may extract facts from the pastsession and ask the current user to correctly answer a question based onthe facts. In the example of display 500, the system asks the user toindicate who the user messaged last night at 6:17 p.m. The example ofdisplay 500 includes a multiple choice challenge, but could also use atext box type of response. Other types of fact questions that can beformulated from a past session include “What restaurant did you make areservation at on Friday?” and “Which image did you share via socialmedia most recently?” Other types of high-level content-based challengesmay be derived from aggregated usage data. For example, the system maydetermine which contact the user messages most often, which places theuser reserves most frequently, etc. In generating sub-challenges, thesystem may include challenges that are diverse across applications andin terms of entity types. In other words, the system may ensure that thesub-challenges represent a variety of applications and/or entitiesconsidered typical for the user.

Returning to FIG. 3 , the system may determine whether the presentedchallenge is met (325). As indicated above, the challenge may includemultiple sub-challenges, depending on the implementation. If thechallenge is not met (325, No), the system may determine whether topresent another challenge (335). For example, the system may provide auser who failed the first challenge another opportunity with a newchallenge (335, Yes), but may not provide a third opportunity (335, No).In some implementations, especially when the challenge already includedsub-challenges, the system may not provide any additional opportunitiesto meet another challenge (335, No). When there are no other challengeopportunities (335, No), the device may enter a lock mode (340). In thelock mode, the device may prevent access to most applications andactivities. For example, the device may enable emergency calling onlyand disable all other access. In another example, the device may send acommunication to a user email address or other user identifierassociated with the device indicating the location where the deviceentered the lock mode. In some implementations, the device may beunlocked when the device is located at a trusted location and the userprovides a password. For example, a user profile may include trustedlocations, such as the user's home or work. When the user is at home orwork (e.g., based on global positioning coordinates), the device mayallow a user to enter a password to unlock the device. This may enable alegitimate user who accidently locked the device to unlock the devicewithout having to contact customer support. In some implementations,unlocking the device may require identity verification, for example viaa call to customer support. In some implementations, unlocking thedevice may require only entry of a password. Other methods of unlockingthe device once locked may also be used.

If the challenge is met (325, Yes), the system may extract features fromthe current session and use the features (e.g., feature vectors for thefeatures) as positive examples to update the classification model (330).In other words, upon successful completion of a challenge, the systemmay train the classification model to recognize the current activity asconsistent with the user's behavior. The system may continue to analyzeand classify sessions until a user stops the inference mode or until thedevice is locked.

FIG. 6 illustrates a flow diagram of an example process 600 for traininga classification model, in accordance with disclosed implementations.Process 600 may be executed by a mobile content-based security system,such as system 100. Process 600 may collect information while the deviceis used in a trusted environment and use the information to train theclassification model to recognize activity consistent with the userprofile. The classification model can be a binary classifier thatindicates whether captured content, e.g., information on a particularscreen capture image, or a sequence of such images, is consistent with aactivity of a device owner. In other implementations, the classificationmodel may be a multi-class classifier trained to determine which userprofile of multiple profiles, if any, the particular screen captureimage or sequence of images is most consistent with. If a multi-classclassifier, the model is trained using multiple training sessions, onefor each user profile the model is trained to recognize. Thus, whileprocess 600 as illustrated is for a binary classifier, it may beexecuted for each different user of a mobile device to train amulti-class classifier model.

Process 600 begins with a determination of whether the device is in atrusted environment (605). A trusted environment is an environment wherethere is a high confidence that the user of the device is the truedevice owner. Determining whether the environment is a trustedenvironment may be dependent on a number of factors, alone or incombination. For example, the user may provide a password that enablesthe training mode. As another example, the user profile may includelocations that are trusted, such as the home or office of the user. Thedevice can determine using GPS coordinates or a wireless networkidentifier whether the current location matches one of the trustedlocations. In some implementations, the trusted environment may requirea successful password unlock (e.g., awaking the device from a sleepingor inactive mode) as well as a match of a trusted location. If thedevice is not in a trusted environment (605, No), no training data iskept. Once the device is in a trusted environment (605, Yes), the systemmay begin capturing screen content (610). As indicated above, thecapture of screen content may take place at regular intervals, each timethe user interacts with the device, upon an explicit command from theuser, etc. The screen information thus represents the informationrendered by an application running on the device. The system maycontinue capturing content (615, No) until a session is complete (615,Yes). A session can be defined as a single screen capture event (APIcall or screen capture image). Thus, one screen capture image may resultin the session being complete. As another example, a session may bedefined as a series of screen capture events. For example, the screencapture events occurring in a specified window, events occurring duringa specific activity, events occurring in a single applications, orevents occurring during use of a single interface, etc. When a sessionis complete (615, Yes), the system may extract and annotate sessionfeatures. Features may be anything recognized in the content associatedwith the session as well as metadata about the content. For example,features can include the program that rendered the content, the locationof the mobile device, the motion of the mobile device, the words,pictures, and logos recognized in the content, the entities (e.g., fromthe knowledge base) identified in the content, etc. The informationabout a particular feature may be represented by a corresponding featurevector, and the feature vectors may be combined (concatenated) in anaggregated feature vector for a single screen or for a session. Thefeature vectors may be considered positive examples of activity for theuser. In other words, the screens can be parsed and annotated aspositive training examples of the type of activity typical for the user.

The system may determine whether there are enough positive examples totrain the classifier (625). For example, the system may require aminimum amount of time (e.g., a couple of weeks, a minimum number ofhours) to observe enough behavior in a trusted environment to ensure auseful classification model. As another example, the system may requirea minimum number of positive examples, or some combination of a minimumnumber of positive examples and a minimum amount of time in trainingmode. Until the minimum criteria is met (625, No) the system continuescollecting information (features) when the device is in a trustedenvironment. Once the minimum criteria is met (625, Yes), the system mayget negative examples. The negative examples may be a generic set ofnegative examples or may be generated by randomly but realisticallypermuting positive examples (630). Permuting positive examples caninclude replacing some of the words/entities in captured content withsimilar words/entities. As one example, a place or person may bereplaced with another place or person. In a multi-classifier modelpermuting positive examples includes using positive examples for oneuser as the negative examples for another user The system may then usethe positive and negative examples to train the classifier (635). Insome implementations, the system may train the classifier without anynegative examples. The system may determine whether the trainingcriteria is met. The training criteria may be, for example a minimumamount of time, a minimum number of positive examples, as describedabove or a minimum classification accuracy. For example, the system mayuse some examples to train the model, and then run the model againstother examples (or the same examples), to determine how well the modelclassifies the known examples. In some implementations, a minimum numberof examples may be used to train the classifier, and then anotherminimum may be collected and used to evaluate the model. Someimplementations may use a combination of a minimum time period, aminimum number of examples and a minimum classification accuracy as thetraining criteria. Until the training criteria is met (640, No) thesystem continues collecting information (features) when the device is ina trusted environment. Once the training criteria is met (640, Yes),process 600 then ends the model is ready for use in an inference mode.However, the system may continue to train the classification model usingnew positive examples. In some implementations, training may continuecontinuously for a minimum period of time (when in a trustedenvironment) or the system may train the model when the usersuccessfully meet a challenge with the session information that promptedthe challenge. In addition, the system may enter a training mode atcertain intervals when the device is in a trusted environment. Thus, thesystem may refine the model and keep it current as the user engages innew activities.

FIG. 7 illustrates a flow diagram of an example process 700 for usingscreen-analysis to enhance device security in a multi-user environment,in accordance with disclosed implementations. Process 700 may beperformed by a mobile content-based security system, such as system 100of FIG. 1 or FIG. 2 . Process 700 may be used to provide unobtrusivesecurity or backup security in a mobile environment, as well asautomatically initiating (e.g., without a specific instruction) aprofile switch in a multi-user environment. Process 700 may begin bytraining a profile classification model to identify and classifymultiple different profiles (705). The training is accomplished usingcontent recognized in screens when the device is in a trustedenvironment, as described above with regard to FIG. 6 . In a profileclassification model, each training session, and thus the positiveexamples generated, is associated with a specific user. Thus, the modelis able to learn activities typical for each user. Accordingly theprofile classification model can be any type of multiple classifier.

Once two or more profiles are sufficiently trained, the system may enteran inference mode. In an inference mode, the system may observe contentin a screen or series of screens, in other words a session, and classifythe session using the trained model (710). In observing the content, thesystem may perform various types of recognition on a screen captureimage, the image having been rendered by an application, e.g., a mobileapplication, a web-based application, or another type of application, oron captured text. The system may then determine feature vectors of thecontent and provide the feature vectors to the classification model. Theclassification model provides a determination of whether the features(e.g., as represented by the feature vectors) match a profile or not.The determination may include a confidence level, which represents howcertain the model is that the input (the feature vector) is consistentwith a particular profile. Thus, for example, the determination mayindicate that the input matches a first user profile with a 70%confidence score and matches a second user profile with a 50% confidencescore.

The system may determine whether the model returns a low confidence forthe signed-on user (715). A low confidence may be measured against athreshold, for example failing to meet a threshold. A low confidence mayindicate that the current activity is not consistent with the signed-onuser. If the confidence is not low (715, No), the system may continueclassifying actions (710). If the confidence is low (715, Yes), thesystem may then determine whether the current activity matches a profilefor another user (720). Whether the activity, e.g. the feature vectorsgenerated from the content displayed on the screen, are consistent witha profile depends on the confidence score of a particular profilemeeting or exceeding a threshold. If the system determines that at leastone confidence score for another user profile (e.g., different than thesigned-in user) does meet or exceed a threshold, the system maydetermine that there is a profile match (720, Yes). The system may theninitiate a profile switch (725).

In some implementations, initiating the profile switch is automatic. Inother words, the system may sign the current user out and sign the otheruser on, which results in use of different user profile data. Automaticprofile switching may be an option expressly selected by the users ofthe mobile device. In some implementations, initiating the profileswitch may include providing a prompt requesting permission to switchuser profiles. For example, the system may provide a window askingwhether the device should switch profiles and inform the user whichprofile will be selected. In some implementations, initiating a profileswitch may sign the current user off and take the device to a sign-ininterface, where the user is required to select a profile and enter apassword, for example. In some implementations, the system may select adefault profile (e.g., the one with the highest confidence score) andprompt for the password. In other words, the system may automaticallylog out of the current profile, which requires the user to expresslysign back in with another profile. Initiating a profile switch may endprocess 700. After a successful switch (e.g., the user successfullysigns in), the system may enter a training phase (e.g., step 705) or maycontinue at step 710 comparing current activity against the new userprofile.

If the current activity does not match another profile (720, No), thesystem may present a challenge to the user (730), as explained abovewith regard to step 320 of FIG. 3 . The challenge may be based onpreviously accessed content that was consistent (e.g. met or exceededthe confidence threshold) with either the profile of the currentlylogged in user or with a profile that had the highest confidence scorefrom step 710. For example, in a multi-user environment, each user mayhave an individual screen capture index, session features, profile data,etc. Thus, the device can select information from the session features,such as session features 132 of FIG. 1 , or the screen capture index,such as index 146 of FIG. 1 , associated with the signed-in user toformulate the challenge as discussed above. The system may also use thesession features and/or screen capture index associated with a profilethat received the highest confidence level rather than the signed inuser. The system may select the profile with the highest confidencelevel when the confidence score for the profile approaches thethreshold, but is not high enough to meet the threshold. Thus, thechallenge may be tailored to the most likely user rather than the signedin user. As indicated above, the challenge may be a series ofsub-challenges and can be based on content recognized in a previouslyviewed screen. In some implementations, rather than presenting achallenge, the system may log the current user off.

If a challenge is presented and met (735, Yes), the system may use thefeature vectors generated for the session as a positive training example(740). If the challenge was based on content associated with thecurrently signed in user, the examples may be associated with thecurrently signed in user. If the challenge is based on contentassociated with another user, the examples may be associated with theother user, and the device may initiate a profile switch, as describedabove. The new training examples may be used to train/refine theclassification model. Process 700 then continues in the inference modefor the currently signed in user.

If the challenge is not met (735, No), the system may determine whetherto issue another challenge (745). As described above with regard to FIG.3 , this may be dependent on the implantation and whether the challengeincludes sub-challenges and whether the user has successfully met anyprevious sub-challenges. If there are no other challenges to be met(745, No), the system may lock the mobile device (750) as describedabove with regard to step 340 of FIG. 3 .

FIG. 8 shows an example of a generic computer device 800, which may beoperated as server 170, and/or device 110 of FIG. 1 , which may be usedwith the techniques described here. Computing device 800 is intended torepresent various example forms of computing devices, such as laptops,desktops, workstations, personal digital assistants, cellulartelephones, smartphones, tablets, servers, and other computing devices,including wearable devices. The components shown here, their connectionsand relationships, and their functions, are meant to be examples only,and are not meant to limit implementations of the inventions describedand/or claimed in this document.

Computing device 800 includes a processor 802, memory 804, a storagedevice 806, and expansion ports 810 connected via an interface 808. Insome implementations, computing device 800 may include transceiver 846,communication interface 844, and a GPS (Global Positioning System)receiver module 848, among other components, connected via interface808. Device 800 may communicate wirelessly through communicationinterface 844, which may include digital signal processing circuitrywhere necessary. Each of the components 802, 804, 806, 808, 810, 840,844, 846, and 848 may be mounted on a common motherboard or in othermanners as appropriate.

The processor 802 can process instructions for execution within thecomputing device 800, including instructions stored in the memory 804 oron the storage device 806 to display graphical information for a GUI onan external input/output device, such as display 816. Display 816 may bea monitor or a flat touchscreen display. In some implementations,multiple processors and/or multiple buses may be used, as appropriate,along with multiple memories and types of memory. Also, multiplecomputing devices 800 may be connected, with each device providingportions of the necessary operations (e.g., as a server bank, a group ofblade servers, or a multi-processor system).

The memory 804 stores information within the computing device 800. Inone implementation, the memory 804 is a volatile memory unit or units.In another implementation, the memory 804 is a non-volatile memory unitor units. The memory 804 may also be another form of computer-readablemedium, such as a magnetic or optical disk. In some implementations, thememory 804 may include expansion memory provided through an expansioninterface.

The storage device 806 is capable of providing mass storage for thecomputing device 800. In one implementation, the storage device 806 maybe or include a computer-readable medium, such as a floppy disk device,a hard disk device, an optical disk device, or a tape device, a flashmemory or other similar solid state memory device, or an array ofdevices, including devices in a storage area network or otherconfigurations. A computer program product can be tangibly embodied insuch a computer-readable medium. The computer program product may alsoinclude instructions that, when executed, perform one or more methods,such as those described above. The computer- or machine-readable mediumis a storage device such as the memory 804, the storage device 806, ormemory on processor 802.

The interface 808 may be a high speed controller that managesbandwidth-intensive operations for the computing device 800 or a lowspeed controller that manages lower bandwidth-intensive operations, or acombination of such controllers. An external interface 840 may beprovided so as to enable near area communication of device 800 withother devices. In some implementations, controller 808 may be coupled tostorage device 806 and expansion port 814. The expansion port, which mayinclude various communication ports (e.g., USB, Bluetooth, Ethernet,wireless Ethernet) may be coupled to one or more input/output devices,such as a keyboard, a pointing device, a scanner, or a networking devicesuch as a switch or router, e.g., through a network adapter.

The computing device 800 may be implemented in a number of differentforms, as shown in the figure. For example, it may be implemented as astandard server 830, or multiple times in a group of such servers. Itmay also be implemented as part of a rack server system. In addition, itmay be implemented in a computing device, such as a laptop computer 832,personal computer 834, or tablet/smart phone 836. An entire system maybe made up of multiple computing devices 800 communicating with eachother. Other configurations are possible.

FIG. 9 shows an example of a generic computer device 900, which may beserver 170 of FIG. 1 , which may be used with the techniques describedhere. Computing device 900 is intended to represent various exampleforms of large-scale data processing devices, such as servers, bladeservers, datacenters, mainframes, and other large-scale computingdevices. Computing device 900 may be a distributed system havingmultiple processors, possibly including network attached storage nodes,that are interconnected by one or more communication networks. Thecomponents shown here, their connections and relationships, and theirfunctions, are meant to be examples only, and are not meant to limitimplementations of the inventions described and/or claimed in thisdocument.

Distributed computing system 900 may include any number of computingdevices 980. Computing devices 980 may include a server or rack servers,mainframes, etc. communicating over a local or wide-area network,dedicated optical links, modems, bridges, routers, switches, wired orwireless networks, etc.

In some implementations, each computing device may include multipleracks. For example, computing device 980 a includes multiple racks 958a-958 n. Each rack may include one or more processors, such asprocessors 952 a-952 n and 962 a-962 n. The processors may include dataprocessors, network attached storage devices, and other computercontrolled devices. In some implementations, one processor may operateas a master processor and control the scheduling and data distributiontasks. Processors may be interconnected through one or more rackswitches 958, and one or more racks may be connected through switch 978.Switch 978 may handle communications between multiple connectedcomputing devices 900.

Each rack may include memory, such as memory 954 and memory 964, andstorage, such as 956 and 966. Storage 956 and 966 may provide massstorage and may include volatile or non-volatile storage, such asnetwork-attached disks, floppy disks, hard disks, optical disks, tapes,flash memory or other similar solid state memory devices, or an array ofdevices, including devices in a storage area network or otherconfigurations. Storage 956 or 966 may be shared between multipleprocessors, multiple racks, or multiple computing devices and mayinclude a computer-readable medium storing instructions executable byone or more of the processors. Memory 954 and 964 may include, e.g.,volatile memory unit or units, a non-volatile memory unit or units,and/or other forms of computer-readable media, such as a magnetic oroptical disks, flash memory, cache, Random Access Memory (RAM), ReadOnly Memory (ROM), and combinations thereof. Memory, such as memory 954may also be shared between processors 952 a-952 n. Data structures, suchas an index, may be stored, for example, across storage 956 and memory954. Computing device 900 may include other components not shown, suchas controllers, buses, input/output devices, communications modules,etc.

An entire system, such as system 100, may be made up of multiplecomputing devices 900 communicating with each other. For example, device980 a may communicate with devices 980 b, 980 c, and 980 d, and thesemay collectively be known as system 100. As another example, system 100of FIG. 1 may include one or more computing devices 900. Some of thecomputing devices may be located geographically close to each other, andothers may be located geographically distant. The layout of system 900is an example only and the system may take on other layouts orconfigurations.

According to certain aspects of the disclosure, a mobile device includesat least one processor and memory storing instructions that, whenexecuted by the at least one processor, cause the mobile device toperform operations. The operations include identifying content renderedby a mobile application, the content being rendered during a session,generating feature vectors from the content and determining that thefeature vectors do not match a classification model. The operations alsoinclude providing, in response to the determination that the featurevectors do not match the classification model, a challenge configured toauthenticate a user of the mobile device.

This and other aspects can include one or more of the followingfeatures. For example, the session may be a first session and thechallenge is based on a previous session distinct from the firstsession. In such an implementation, the previous session may includefeature vectors that matched the classification model or feature vectorsverified using a trusted location or feature vectors verified by aprevious challenge. As another example, the challenge may be configuredto prompt the user to complete information missing from a screendisplayed by the mobile device in a previous session that includedfeature vectors that matched the classification model. As anotherexample, providing the challenge can include extracting information froma screen displayed by the mobile device in a previous session thatincluded feature vectors matching the classification model andgenerating a multiple choice question based on the extractedinformation.

As another example, the memory may further store instructions that, whenexecuted by the at least one processor, cause the mobile device toreceive a response to the challenge and lock the mobile device when theresponse fails the challenge. As another example, the challenge mayinclude a series of sub-challenges. As another example, theclassification model is trained by sessions occurring at a trustedlocation. A session may include a single screen captured on the mobiledevice, screens captured during usage of a particular user interface inthe mobile application, screens captured during a window of time, orscreens captured during use of the mobile application.

According to certain aspects of the disclosure a method may comprisedetermining that a mobile device is located at a trusted location,capturing information from a session, the information coming fromcontent rendered by a mobile application running on the mobile deviceduring the session, and generating feature vectors for the session. Themethod also includes repeating the capturing and determining until atraining criteria is met and authenticating a user of the mobile deviceusing the trained classification model.

This and other aspects can include one or more of the followingfeatures. For example, the training criteria can include a minimumquantity of sessions or a minimum classification accuracy. As anotherexample, authenticating the user using the trained classification modelmay include determining a current session based on content rendered by amobile application, generating feature vectors for the session, andproviding, in response to determining that the feature vectors do notmatch the classification model, a challenge configured to authenticate auser of the mobile device. In some such implementations, the featurevectors may not match the classification model when a confidence scoregenerated by evaluating the feature vectors with the classificationmodel fails to meet a threshold. As another example, determining themobile device is located at a trusted location may include accessing auser profile associated with the mobile device to determine a trustedlocation and determining that the mobile device is currently located atthe trusted location. In some such implementations, the trusted locationmay be represented by global positioning system (GPS) coordinates andthe mobile device uses current GPS coordinates to determine whether themobile device is current at the trusted location or the trusted locationis represented by a wireless network identifier and the mobile devicedetermines whether a wireless network the mobile device is connected tomatches the wireless network identifier.

According to certain aspects of the disclosure, a mobile devicecomprises at least one processor and memory storing instructions that,when executed by the at least one processor, cause the mobile device toperform operations. The operations may include identifying contentrendered by a mobile application, the content being rendered during asession, and generating feature vectors from the content. The operationsmay also include applying a classification model to the feature vectors,determining whether the feature vectors match a first user profile basedon application of the classification model, the first user profilediffering from a second user profile, the mobile device being currentlyassociated with the second user profile, and initiating a profile switchresponsive to determining that the feature vectors match the first userprofile.

This and other aspects can include one or more of the followingfeatures. For example, the operations may also include determining thatthe feature vectors match no user profiles and providing a challenge achallenge configured to authenticate a user of the mobile device. Asanother example, the challenge may be based on second content renderedduring a previous session associated with the second user profile, thesecond content being associated with feature vectors consistent with thesecond user profile according to the classification model. As anotherexample, the challenge is based on second content rendered during aprevious session associated with the first user profile when theclassification model determines the first user profile has a higherconfidence score than the second user profile with regard to the featurevectors. As another example, determining whether the feature vectorsmatch the first user profile occurs after determining that the featurevectors fail to match the second user profile.

As another example, the operations may also include training theclassification model by determining that a mobile device is located in atrusted environment associated with the second user profile, recognizingcontent rendered by a mobile application running on the mobile device,the content being associated with a session generating feature vectorsfor the content, repeating the recognizing and generating for at least aminimum quantity of sessions, and training the classification modelusing the feature vectors as positive examples, the positive examplesbeing associated with the second user profile. In some suchimplementations, positive examples associated with the first userprofile are used as negative examples for the second user profile intraining the classification model. The operations may also includetraining the classification model until a minimum classificationaccuracy is reached.

Various implementations can include implementation in one or morecomputer programs that are executable and/or interpretable on aprogrammable system including at least one programmable processor, whichmay be special or general purpose, coupled to receive data andinstructions from, and to transmit data and instructions to, a storagesystem, at least one input device, and at least one output device.

These computer programs (also known as programs, software, softwareapplications or code) include machine instructions for a programmableprocessor, and can be implemented in a high-level procedural and/orobject-oriented programming language, and/or in assembly/machinelanguage. As used herein, the terms “machine-readable medium”“computer-readable medium” refers to any non-transitory computer programproduct, apparatus and/or device (e.g., magnetic discs, optical disks,memory (including Read Access Memory), Programmable Logic Devices(PLDs)) used to provide machine instructions and/or data to aprogrammable processor.

The systems and techniques described here can be implemented in acomputing system that includes a back end component (e.g., as a dataserver), or that includes a middleware component (e.g., an applicationserver), or that includes a front end component (e.g., a client computerhaving a graphical user interface or a Web browser through which a usercan interact with an implementation of the systems and techniquesdescribed here), or any combination of such back end, middleware, orfront end components. The components of the system can be interconnectedby any form or medium of digital data communication (e.g., acommunication network). Examples of communication networks include alocal area network (“LAN”), a wide area network (“WAN”), and theInternet.

The computing system can include clients and servers. A client andserver are generally remote from each other and typically interactthrough a communication network. The relationship of client and serverarises by virtue of computer programs running on the respectivecomputers and having a client-server relationship to each other.

A number of implementations have been described. Nevertheless, variousmodifications may be made without departing from the spirit and scope ofthe invention. In addition, the logic flows depicted in the figures donot require the particular order shown, or sequential order, to achievedesirable results. In addition, other steps may be provided, or stepsmay be eliminated, from the described flows, and other components may beadded to, or removed from, the described systems. Accordingly, otherimplementations are within the scope of the following claims.

What is claimed is:
 1. A method implemented by one or more processors,the method comprising: identifying a user profile that corresponds to auser and that is active for an electronic device; determining whethercurrent activity of the electronic device, while the user profile isactive for the electronic device, matches the user profile, whereindetermining whether the current activity of the electronic devicematches the user profile comprises: processing, using a classificationmodel, features corresponding to interactive user activity on theelectronic device to determine whether the features corresponding to theinteractive user activity on the electronic device match one or morefeatures of at least one previous period of interactive user activityindicated by the user profile, wherein the interactive user activityincludes at least application activity occurring on the electronicdevice during one or more user interactions with the electronic device;in response to determining the features corresponding to the interactiveuser activity on the electronic device do not match the one or morefeatures of the at least one previous period of interactive useractivity indicated by the user profile: determining whether the currentactivity of the electronic device, while the user profile is active forthe electronic device, matches an additional user profile, of aplurality of additional user profiles, the additional user profilecorresponding to an additional user, wherein determining whether thecurrent activity of the electronic device, while the user profile isactive for the electronic device, matches the additional user profilethat corresponds to the additional user comprises: processing, using theclassification model, the features corresponding to the interactive useractivity on the electronic device to determine whether the featurescorresponding to the interactive user activity on the electronic devicematch one or more additional features of at least one additionalprevious period of interactive user activity indicated by the additionaluser profile that corresponds to the additional user; and in response todetermining the current activity of the electronic device matches theadditional user profile: initiating a profile switch, to the additionaluser profile, at the electronic device.
 2. The method of claim 1,further comprising: in response to determining the featurescorresponding to the interactive user activity on the electronic devicedo not match one or more features of at least one additional previousperiod of interactive user activity indicated by the additional userprofile: determining whether the current activity of the electronicdevice, while the user profile is active for the electronic device,matches a further additional user profile, of the plurality ofadditional user profiles, the further additional user profilecorresponding to a further additional user; and in response todetermining the current activity of the user device matches the furtheradditional user profile: initiating the profile switch, to the furtheradditional user profile, at the electronic device.
 3. The method ofclaim 2, wherein determining whether the current activity of theelectronic device matches the further additional user profile comprises:processing, using the classification model, the features correspondingto the interactive user activity on the electronic device to determinewhether the features corresponding to the interactive user activity onthe electronic device match one or more features of at least one furtheradditional previous period of interactive user activity indicated by thefurther additional user profile.
 4. The method of claim 1, whereindetermining whether the current activity of the electronic devicematches the user profile is in response to determining that the currentactivity at the electronic device corresponds to outlier activity forthe user profile.
 5. The method of claim 1, wherein initiating theprofile switch at the electronic device comprises: automatically signingout of the user profile to deactivate the user profile at the electronicdevice; and automatically signing in to the additional user profile toactivate the additional user profile at the electronic device.
 6. Themethod of claim 1, wherein initiating the profile switch at theelectronic device comprises: automatically signing out of the userprofile to deactivate the user profile at the electronic device; andcausing a sign-in user interface to be visually rendered at theelectronic device to enable the additional user to sign-in to theadditional user profile.
 7. The method of claim 6, further comprising:in response to visually rendering the sign-in interface at theelectronic device: receiving, at the electronic device, credentials tosign-in to the additional user profile; and signing in to the additionaluser profile based on the credentials.
 8. The method of claim 1, whereininitiating the profile switch at the electronic device comprises:causing a prompt to be visually rendered at the electronic device torequest permission to switch to the additional user profile associatedwith the additional user.
 9. The method of claim 8, further comprising:in response to visually rendering the prompt at the electronic device:receiving, at the electronic device, user input to permit switching tothe additional user profile.
 10. A system comprising: at least oneprocessor; and at least one memory storing instructions that, whenexecuted, cause the at least one processor to: identify a user profilethat corresponds to a user and that is active for an electronic device;determine whether current activity of the electronic device, while theuser profile is active for the electronic device, matches the userprofile, wherein the instructions to determine whether the currentactivity of the electronic device matches the user associated with theuser profile comprise instructions to: process, using a classificationmodel, features corresponding to interactive user activity on theelectronic device to determine whether the features corresponding to theinteractive user activity on the electronic device match one or morefeatures of at least one previous period of interactive user activityindicated by the user profile, wherein the interactive user activityincludes at least application activity occurring on the electronicdevice during one or more user interactions with the electronic device;in response to determining the features corresponding to the interactiveuser activity on the electronic device do not match the one or morefeatures of the at least one previous period of interactive useractivity indicated by the user profile: determine whether the currentactivity of the electronic device, while the user profile is active forthe electronic device, matches an additional user profile, of aplurality of additional user profiles, the additional user profilecorresponding to an additional user, wherein determining whether thecurrent activity of the electronic device, while the user profile isactive for the electronic device, matches the additional user profilethat corresponds to the additional user comprises: processing, using theclassification model, the features corresponding to the interactive useractivity on the electronic device to determine whether the featurescorresponding to the interactive user activity on the electronic devicematch one or more additional features of at least one additionalprevious period of interactive user activity indicated by the additionaluser profile that corresponds to the additional user; and in response todetermining the current activity of the electronic device matches theadditional user profile: initiate a profile switch, to the additionaluser profile, at the electronic device.
 11. The system of claim 10,wherein the instructions further comprise instructions to: in responseto determining the features corresponding to the interactive useractivity on the electronic device do not match one or more features ofat least one additional previous period of interactive user activityindicated by the additional user profile: determine whether the currentactivity of the electronic device, while the user profile is active forthe electronic device, matches a further additional user profile, of theplurality of additional user profiles, the further additional userprofile corresponding to a further additional user; and in response todetermining the current activity of the user device matches the furtheradditional user profile: initiate the profile switch, to the furtheradditional user profile, at the electronic device.
 12. The system ofclaim 11, wherein the instructions to determine whether the currentactivity of the electronic device matches the further additional userprofile comprise instructions to: process, using the classificationmodel, the features corresponding to the interactive user activity onthe electronic device to determine whether the features corresponding tothe interactive user activity on the electronic device match one or morefeatures of at least one further additional previous period ofinteractive user activity indicated by the further additional userprofile.
 13. The system of claim 10, wherein determining whether thecurrent activity of the electronic device matches user profile is inresponse to determining that the current activity at the electronicdevice corresponds to outlier activity for the user profile.
 14. Thesystem of claim 10, wherein the instructions to initiate the profileswitch at the electronic device comprise instructions to: automaticallysign out of the user profile to deactivate the user profile at theelectronic device; and automatically sign in to the additional userprofile to activate the additional user profile at the electronicdevice.
 15. The system of claim 10, wherein the instructions to initiatethe profile switch at the electronic device comprise instructions to:automatically sign out of the user profile to deactivate the userprofile at the electronic device; and cause a sign-in user interface tobe visually rendered at the electronic device to enable the additionaluser to sign-in to the additional user profile.
 16. The system of claim10, the instructions to initiate the profile switch at the electronicdevice comprise instructions to: cause a prompt to be visually renderedat the electronic device to request permission to switch to theadditional user profile associated with the additional user.
 17. Anon-transitory computer-readable storage medium storing instructionsthat, when executed, cause at least one processor to execute theinstructions, the instructions causing the at least one processor to:identify a user profile that corresponds to a user and that is activefor an electronic device; determine whether current activity of theelectronic device, while the user profile is active for the electronicdevice, matches the user profile, wherein the instructions to determinewhether the current activity of the electronic device matches the userprofile comprise instructions to: process, using a classification model,features corresponding to interactive user activity on the electronicdevice to determine whether the features corresponding to theinteractive user activity on the electronic device match one or morefeatures of at least one previous period of interactive user activityindicated by the user profile, wherein the interactive user activityincludes at least application activity occurring on the electronicdevice during one or more user interactions with the electronic device;in response to determining the features corresponding to the interactiveuser activity on the electronic device do not match the one or morefeatures of the at least one previous period of interactive useractivity indicated by the user profile: determine whether the currentactivity of the electronic device, while the user profile is active forthe electronic device, matches an additional user profile, of aplurality of additional user profiles, the additional user profilecorresponding to an additional user, wherein determining whether thecurrent activity of the electronic device, while the user profile isactive for the electronic device, matches the additional user profilethat corresponds to the additional user comprises: processing, using theclassification model, the features corresponding to the interactive useractivity on the electronic device to determine whether the featurescorresponding to the interactive user activity on the electronic devicematch one or more additional features of at least one additionalprevious period of interactive user activity indicated by the additionaluser profile that corresponds to the additional user; and in response todetermining the current activity of the electronic device matches theadditional user profile: initiating a profile switch, to the additionaluser profile, at the electronic device.